ALPHA-DEUTERIUM KINETIC ISOTOPE EFFECTS IN REACTIONS OF METHYLLITHIUM- IS BETTER AGGREGATION THE CAUSE OF LOWER REACTIVITY

The values k(H)/k(D) for alpha-deuterium kinetic isotope effects for t he reaction of methyllithium and methylmagnesium iodide with a series of substrates are consistently ca. 10-15% higher for the lithium reage nt than for the Grignard reagent. This may indicate a pre-equilibrium between an aggregate and a reactive monomer, with a better fit of the trideuterio monomer in the aggregate. An attempt has been made to comp are the equilibrium constants for the aggregation of deuterio and prot io methyllithium by studying the metal-halogen equilibrium between met hyllithium and methyl iodide.